Aminoxyl denotes a

radical Radical (from Latin: ', root) may refer to: Politics and ideology Politics *Classical radicalism, the Radical Movement that began in late 18th century Britain and spread to continental Europe and Latin America in the 19th century *Radical politics ...

functional group with general structure R₂N–O^•. It is commonly known as a nitroxyl radical or a nitroxide, however

IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...

discourages the use of these terms, as they erroneously suggest the presence of a

nitro group In organic chemistry, nitro compounds are organic compounds that contain one or more nitro functional groups (). The nitro group is one of the most common explosophores (functional group that makes a compound explosive) used globally. The nit ...

. Aminoxyls are structurally related to

hydroxylamines Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula . The compound exists as hygroscopic colorless crystals.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Prof ...

and ''N''-oxoammonium salts, with which they can interconvert via a series of

redox Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...

steps. Aminoxyl radical.svg, The general structure of the aminoxyl radical 2,2,6,6-Tetramethylpiperidinyloxyl.svg,

TEMPO In musical terminology, tempo (Italian for 'time'; plural 'tempos', or from the Italian plural), measured in beats per minute, is the speed or pace of a given musical composition, composition, and is often also an indication of the composition ...

, a commonly encountered organic aminoxyl radical Kaliumnitrosodisulfonat.svg, Fremy's salt, an inorganic aminoxyl radical Sterically unhindered aminoxyls bearing α-hydrogens are unstable and undergo rapid

disproportionation In chemistry, disproportionation, sometimes called dismutation, is a redox reaction in which one compound of intermediate oxidation state converts to two compounds, one of higher and one of lower oxidation state. The reverse of disproportionatio ...

to nitrones and

hydroxylamine Hydroxylamine (also known as hydroxyammonia) is an inorganic compound with the chemical formula . The compound exists as hygroscopic colorless crystals.Greenwood and Earnshaw. ''Chemistry of the Elements.'' 2nd Edition. Reed Educational and Prof ...

s. Sterically hindered aminoxyls without α-hydrogens, such

and TEMPOL, and are persistent (stable) radicals and find use in a range of applications, both on the laboratory scale and in industry. Their ability to reversibly bind to other radical compounds makes them important as both

spin label A spin label (SL) is an organic molecule which possesses an unpaired electron, usually on a nitrogen atom, and the ability to bind to another molecule. Spin labels are normally used as tools for probing proteins or biological membrane-local dynami ...

s and spin traps. They are used to selectively oxidise carbonyl groups via oxoammonium-catalyzed oxidations. They are also used as

polymer stabilizers Polymer stabilizers (British English: polymer stabilisers) are chemical additives which may be added to polymeric materials to inhibit or retard their degradation. Mainly they protect plastic and rubber products against heat, oxidation, and UV light ...

such as

hindered amine light stabilizers Hindered amine light stabilizers (HALS) are chemical compounds containing an amine functional group that are used as stabilizers in plastics and polymers. These compounds are typically derivatives of tetramethylpiperidine and are primarily used ...

or as transient reactive species in ''p''-phenylenediamine based

antiozonant An antiozonant, also known as anti-ozonant, is an organic compound that prevents or retards damage caused by ozone. The most important antiozonants are those which prevent degradation of elastomers like rubber. A number of research projects stud ...

s. They are used both to form polymers via nitroxide-mediated radical polymerization and prevent their formation as

polymerization inhibitor In polymer chemistry, polymerisation inhibitors (US: polymerization inhibitors) are chemical compounds added to monomers to prevent their self-polymerisation. Unsaturated monomers such as acrylates, vinyl chloride, butadiene and styrene require i ...

s. Various other reagents, such as ''N''-hydroxyphthalimide can also be converted into aminoxyl radicals as part of their chemistry.

References

{{Reflist Functional groups Free radicals

See also

References